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scumbag
 
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sealing the fan shroud

I'm planning to build a heat exchanger in the same vein as the Protomotive exchanger shown here. *thank you charlesbahn for posting these pictures.




I also will not be using footwell blowers. So the fan will have to power the whole system as well as cool the engine.

As such, I'm wondering if there is any benefit to be had by sealing the fan shroud to the engine. I realize it'd have to be sealed using an RTV silicone or similar. I feel like maximizing the efficiency of the fan can have no real drawbacks. As my engine is in pieces, I will have unfettered access to the top of the engine to seal the shroud.

Are there any drawbacks to this idea that I'm missing?
Am I massively overthinking this and the fan shroud fit is 'good enough'?
Thanks in advance!
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Old 04-30-2019, 07:06 AM
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New-ish 911SC Targa Owner
 
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could you use some sort of weather stripping with a peel and stick adhesive on one side around all the areas air leaks out? Thinking about the 6 intake runners. A good amount of air comes out there on my car.
Its a good thought so I'm interested in what everyone else says.
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Old 04-30-2019, 07:38 AM
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scumbag
 
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Quote:
Originally Posted by pampadori View Post
could you use some sort of weather stripping with a peel and stick adhesive on one side around all the areas air leaks out? Thinking about the 6 intake runners. A good amount of air comes out there on my car.
Its a good thought so I'm interested in what everyone else says.
I thought about a peel-n-stick seal but worry about the temps. Since it'd be in direct contact with the heads, I figure it needs to be able to tolerate ~300*F to have a margin of safety. I sure don't want a fire.

But I do agree that there are a lot of opportunities for the fan-driven air to escape. I'm still some time from assembling my engine (cams just got to DRC for regrind and heads haven't even gone to the machine shop yet) so we have plenty of time to bench-race this idea before I green-light it and let everyone know what happens.
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Old 04-30-2019, 09:01 AM
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https://www.grainger.com/product/PEMKO-Silicone-2EVA9?cm_sp=Product_Details-_-Products_Based_on_Your_Search-_-IDPPLARECS&cm_vc=IDPPLARECS

This stuff says stays flexible to 450F. i would assume that would do the trick just fine.
pretty good size at .5" by .25" thick.
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'83 Targa 300k w/ freshened 3.0 with 930/52 case and ARP and Raceware hardware - AEM Infinity 506, Triumph T595 throttle bodies, B&B headers, Dynomax muff, Fidanza FW, Alum PP
'05 E500 wagon in minty cond
'13 Volvo XC60 (hers)
Old 04-30-2019, 10:05 AM
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scumbag
 
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^^^available through Amazon as well for less money.
Although the cross-section shows it's teardrop shaped. I imagine it could be made to work with some angled cuts at corners/turns.

I'll add it to my 911 list so I don't have to look for it later.
Well done, sir!
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Old 04-30-2019, 10:10 AM
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Back in the day, I worked with Continental and Mooney Aircraft on their ‘“new” turbocharged engine installation. From the factory the engine was severely temp limited anytime the OAT was above 60F. After hours of consultation with Continental I sealed every air leak in the cooling shrouds. Zero clearance was the tolerance I decided on. It required hours cutting and pop riveting silicone baffling material everywhere ther was a gap or potential leak. After the work, I tested the airplane in flight and on the ground in Mojave area airports during the summer and could climb at rated power at best rate to the service ceiling. Continental sent my process to Mooney to insure that production a/c were properly sealed. That was a TSIO-360 powerplant in a closely cowled plane, right at the maximum heat shedding limits.
My 3.2 will only go above 185F during the summer when going uphill or in slow traffic. That being said any air that is allowed to escape without pulling BTUs out of the engine is slacking. Unless you have your cylinder head instrumented for temp, it’s hard to say how much leakage is ok.
Here is the stuff to use:
https://www.aircraftspruce.com/menus/ap/baffling_0material.html
I still have rolls and sheets for various projects. Make templates from paper and card board to prototype. I was looking at the heat exchanger, probably a bad idea to try and capture the heated air from the oil cooler, you want as large a pressure differential as you can get across a radiator, forcing the exhausted exchanger air out through the heater boxes will cause some back pressures.
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Last edited by ClickClickBoom; 04-30-2019 at 12:51 PM..
Old 04-30-2019, 12:08 PM
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Click Boom - so you are saying the sealing of the aircraft engine worked - lowered the engine temps significantly?

Chris - why rely on the engine fan for all your heating air? Why not put an in-line fan into the system. If you are concerned about stealing engine cooling air (during the winter? Is overheating apt to be an issue in the winter?), just block off the heating air outlets from atop the engine, and draw the air for the fan from somewhere else.

The stock cabin air valves back in the rear will divert all the air which the fan blows into the outlet or outlets for that purpose through the engine mounted blower motor, then through the heat exchangers, either to the cabin, or into the air space back by the transmission, or some combination of the two. In summer, this air, warmed by the heat exchangers,is just vented into the space beneath the chassis by the transmission.
Racers, without heat exchangers on their exhausts, don't have this issue.

Porsche must have had some reason for the air valve to work as it does, with an outlet to the under car space, instead of just a valve which goes from fully open to fully closed. Cooling the exhaust? Why do that? Preventing heat from the exhaust tubing from rising to heat the engine? Racers don't seem to have issues with this.

I don't see the 911 engines as having this much of a thermal issue. Better oil cooling, like a center front radiator, work wonders. Yes, for the periphery of the engine cover you could maybe attach something which would not glue the cover to the engine. But what about where the six manifold runners go through? You'd want to work in the front and rear engine tin as well. Sealing with what amounts to glue is going to complicate future work on the engine.
Old 04-30-2019, 01:25 PM
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scumbag
 
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Walt,
I don’t plan to run HEs; just headers.
I live in the Midwest and plan to drive the car through 3 seasons. So defogging the windscreen and just enough heat to not need gloves in ~40-45 temps is all I’m after. I’m not in need of proper heat like my 4Runner.

The driving ethos of this build is minimalism and lightweight. I realize fans to draw some heat from an already marginal heating system would be a minor concession in weight. But they’d also be a major increase in complication. My planned HVAC controls are a single lever at the parking brake to actuate the heater boxes in the back and that’s it. It’s as simple a system as I could devise and still have some heat. I have a plan if I find the primary fan can’t drive the heat sufficiently.

If the engine fan is powering this system in addition to cooling the engine, maximizing its efficiency would net a better heat source and possibly increase the cooling efficiency of the engine. If I can get away with one fender-mounted oil cooler, less weight and less complication. Increasing the efficiency of the cooling effect of the fan over the engine’s fins would increase the total capacity to cool the engine.
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Old 04-30-2019, 02:24 PM
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Quote:
Originally Posted by Walt Fricke View Post
Click Boom - so you are saying the sealing of the aircraft engine worked - lowered the engine temps significantly?

Chris - why rely on the engine fan for all your heating air? Why not put an in-line fan into the system. If you are concerned about stealing engine cooling air (during the winter? Is overheating apt to be an issue in the winter?), just block off the heating air outlets from atop the engine, and draw the air for the fan from somewhere else.

The stock cabin air valves back in the rear will divert all the air which the fan blows into the outlet or outlets for that purpose through the engine mounted blower motor, then through the heat exchangers, either to the cabin, or into the air space back by the transmission, or some combination of the two. In summer, this air, warmed by the heat exchangers,is just vented into the space beneath the chassis by the transmission.
Racers, without heat exchangers on their exhausts, don't have this issue.

Porsche must have had some reason for the air valve to work as it does, with an outlet to the under car space, instead of just a valve which goes from fully open to fully closed. Cooling the exhaust? Why do that? Preventing heat from the exhaust tubing from rising to heat the engine? Racers don't seem to have issues with this.

I don't see the 911 engines as having this much of a thermal issue. Better oil cooling, like a center front radiator, work wonders. Yes, for the periphery of the engine cover you could maybe attach something which would not glue the cover to the engine. But what about where the six manifold runners go through? You'd want to work in the front and rear engine tin as well. Sealing with what amounts to glue is going to complicate future work on the engine.
Walt,
Yes, my mods were incorporated into the factory designs. Continental stated one square inch of missed seals was enough to cause cooling problems in an aircraft that climbed at 130kts(I think, it’s been a long time ago). The ram air differential is measured in inches of water. If you look at the 935 engine, air control was at the top of the list, power is wonderful, but if you can’t get rid of the excess heat, that very power will kill the engine.
Just a few shots where you can see the shrouding, but around the oil cooler they use some sort of duct tape for sealing.
https://youtu.be/wPfK_BispVo
Control of cooling air is critical.
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1984 Carrera El Chupacabra
1974 Toyota FJ40 Turbo Diesel
"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 04-30-2019, 06:21 PM
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Caveman Hammer Mechanic
 
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Quote:
Originally Posted by chrisbalich View Post
Walt,
I don’t plan to run HEs; just headers.
I live in the Midwest and plan to drive the car through 3 seasons. So defogging the windscreen and just enough heat to not need gloves in ~40-45 temps is all I’m after. I’m not in need of proper heat like my 4Runner.

The driving ethos of this build is minimalism and lightweight. I realize fans to draw some heat from an already marginal heating system would be a minor concession in weight. But they’d also be a major increase in complication. My planned HVAC controls are a single lever at the parking brake to actuate the heater boxes in the back and that’s it. It’s as simple a system as I could devise and still have some heat. I have a plan if I find the primary fan can’t drive the heat sufficiently.

If the engine fan is powering this system in addition to cooling the engine, maximizing its efficiency would net a better heat source and possibly increase the cooling efficiency of the engine. If I can get away with one fender-mounted oil cooler, less weight and less complication. Increasing the efficiency of the cooling effect of the fan over the engine’s fins would increase the total capacity to cool the engine.
That heater box, if it is sealing the output of the oil cooler is a bad design idea. Anything that reduces the differential pressure across a radiator will cause that radiator to be less effective, the reduction in oil cooling is impossible to calculate. If you need heat use an secondary radiator in the oil cooling system up front in the frunk.
The engine fans cooling duties are more for cylinder head/barrel than case mounted oil cooler, so unless you have a secondary cooling radiator in one or both of the fenders, you might overwhelm the cooling system.
It cracks me up when guys use the lower temp thermocouple to control the fans or even better a switch.
A series of radiators have the ability to transfer X amount of BTUs for a given situation, if the oil is too hot there are 2 choices, 1- slow the internal production of heat, 2-melt the motor when the oil fails. Everything else is a placebo.
__________________
1984 Carrera El Chupacabra
1974 Toyota FJ40 Turbo Diesel
"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936

Last edited by ClickClickBoom; 04-30-2019 at 06:34 PM..
Old 04-30-2019, 06:28 PM
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scumbag
 
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Quote:
Originally Posted by ClickClickBoom View Post
That heater box, if it is sealing the output of the oil cooler is a bad design idea. Anything that reduces the differential pressure across a radiator will cause that radiator to be less effective, the reduction in oil cooling is impossible to calculate. If you need heat use an secondary radiator in the oil cooling system up front in the frunk.
The engine fans cooling duties are more for cylinder head/barrel than case mounted oil cooler, so unless you have a secondary cooling radiator in one or both of the fenders, you might overwhelm the cooling system.
It cracks me up when guys use the lower temp thermocouple to control the fans or even better a switch.
A series of radiators have the ability to transfer X amount of BTUs for a given situation, if the oil is too hot there are 2 choices, 1- slow the internal production of heat, 2-melt the motor when the oil fails. Everything else is a placebo.
I have an aftermarket oil cooler in the passenger fender. It's not yet ducted or blocked off like the Carrera cooler. But it came with the car and I've had bigger fish to fry thus far in the build.

The heater box on the engine-mounted oil cooler is not my idea and was put into production by Protomotive on turbo-converted 911 engines. I reckon they make way more heat than my 9.3:1 3.0L with cams will.

The rest of the on-engine cooling system remains unchanged from factory (aside from my proposed shroud sealing) so there would be even more air moving across the cylinders and heads if the oil cooler heater box stalls/slows the air moving through it.

I'm not sure I follow you about fans not aiding the shedding of heat from a radiator. I'm not an engineer, so all of my knowledge is based on practical experience more so than theory, but my understanding of heat transfer is that it (in this instance) is partially dependent on the difference between the temperature of the radiator and ambient. The fan ensures ambient doesn't climb (heat soak) during stationary/low-speed intervals while the engine runs and subsequently makes the radiator's efficiency more consistent. A fan will never lower true ambient, but will help stave off heat soak. I just don't see how that's a bad thing.
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Old 05-01-2019, 04:30 AM
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Caveman Hammer Mechanic
 
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Quote:
Originally Posted by chrisbalich View Post
I have an aftermarket oil cooler in the passenger fender. It's not yet ducted or blocked off like the Carrera cooler. But it came with the car and I've had bigger fish to fry thus far in the build.

The heater box on the engine-mounted oil cooler is not my idea and was put into production by Protomotive on turbo-converted 911 engines. I reckon they make way more heat than my 9.3:1 3.0L with cams will.

The rest of the on-engine cooling system remains unchanged from factory (aside from my proposed shroud sealing) so there would be even more air moving across the cylinders and heads if the oil cooler heater box stalls/slows the air moving through it.

I'm not sure I follow you about fans not aiding the shedding of heat from a radiator. I'm not an engineer, so all of my knowledge is based on practical experience more so than theory, but my understanding of heat transfer is that it (in this instance) is partially dependent on the difference between the temperature of the radiator and ambient. The fan ensures ambient doesn't climb (heat soak) during stationary/low-speed intervals while the engine runs and subsequently makes the radiator's efficiency more consistent. A fan will never lower true ambient, but will help stave off heat soak. I just don't see how that's a bad thing.
Bingo,
My point is any radiator has a given ability to reject heat. Coolant/radiator temp, Outside Air Temp and flow of coolant medium(air volume and speed) will determine the cooling ability. Without knowing the actual engineering numbers for all the coolers involved, the Promotive use of the engine mounted oil cooler for a heat source is an engineering unknown. The flow of air through the oil cooler and across the heads/barrels is an engineering design. Changing that design randomly leads you down a path of unknown direction. Aircraft manufacturers spend enormous amounts time and rescources controlling airflow, for cooling and otherwise. Cylinder heads have an optimal operating temperature range, without having access to the manufacturers design intent, changing the design of the cooling airflow is an experiment at best. Without instrumenting the engine to determine the actual cooling is problematic at best. The road of unintended consequences is full of sharp turns and potholes. Porsche has swerved around these over the years, fixing and changing the design to meet the market. Porsche designed the fan system with a specific area of exhaust for that fan, changing that area unresearched is dubious.
In summary, changing design intent, without engineering research is fraught with failure possibilities. The 64 million dollar question is, if it was a good design idea, why didn't Porsche implement the design in question?
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1984 Carrera El Chupacabra
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"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 05-01-2019, 10:43 AM
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scumbag
 
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Quote:
Originally Posted by ClickClickBoom View Post
Bingo,
My point is any radiator has a given ability to reject heat. Coolant/radiator temp, Outside Air Temp and flow of coolant medium(air volume and speed) will determine the cooling ability. Without knowing the actual engineering numbers for all the coolers involved, the Promotive use of the engine mounted oil cooler for a heat source is an engineering unknown. The flow of air through the oil cooler and across the heads/barrels is an engineering design. Changing that design randomly leads you down a path of unknown direction. Aircraft manufacturers spend enormous amounts time and rescources controlling airflow, for cooling and otherwise. Cylinder heads have an optimal operating temperature range, without having access to the manufacturers design intent, changing the design of the cooling airflow is an experiment at best. Without instrumenting the engine to determine the actual cooling is problematic at best. The road of unintended consequences is full of sharp turns and potholes. Porsche has swerved around these over the years, fixing and changing the design to meet the market. Porsche designed the fan system with a specific area of exhaust for that fan, changing that area unresearched is dubious.
In summary, changing design intent, without engineering research is fraught with failure possibilities. The 64 million dollar question is, if it was a good design idea, why didn't Porsche implement the design in question?
Well said and I'm with you 100%.
My position on your proposed question, "Why didn't Porsche implement the design in question?" is that they wanted 4 season heat, not just defogging capabilities. Hence the Porsche heat exchanger system and the engine-mounted blower to maintain heat in the cabin at idle. As I've decreased the cabin-heating requirements, I'm decreasing the system that supplies heat to the cabin. The Protomotive HE has been in use for some time on engines with higher output than mine. I have been unable to find any drawbacks to the system aside from decreased output of cabin heat. As such, I feel that it will work fine for my intended purposes.

My query about sealing the shroud was to see if anyone had tried and what the consequences were. I'm not trying to blaze any new trails here. I'm making sure I've done a thorough survey of what does and doesn't work before I make decisions for my car.

Thank you very much for all your insight. I do love this board and its members for their openness and willingness to help.
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Old 05-01-2019, 11:00 AM
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Quote:
Originally Posted by chrisbalich View Post
Well said and I'm with you 100%.
My position on your proposed question, "Why didn't Porsche implement the design in question?" is that they wanted 4 season heat, not just defogging capabilities. Hence the Porsche heat exchanger system and the engine-mounted blower to maintain heat in the cabin at idle. As I've decreased the cabin-heating requirements, I'm decreasing the system that supplies heat to the cabin. The Protomotive HE has been in use for some time on engines with higher output than mine. I have been unable to find any drawbacks to the system aside from decreased output of cabin heat. As such, I feel that it will work fine for my intended purposes.

My query about sealing the shroud was to see if anyone had tried and what the consequences were. I'm not trying to blaze any new trails here. I'm making sure I've done a thorough survey of what does and doesn't work before I make decisions for my car.

Thank you very much for all your insight. I do love this board and its members for their openness and willingness to help.
Do seal the shroud, absolutely no downside!
Cheers
eric
__________________
1984 Carrera El Chupacabra
1974 Toyota FJ40 Turbo Diesel
"Easy, easy, this car is just the right amount of chitty"
"America is all about speed. Hot,nasty, bad ass speed."
Eleanor Roosevelt, 1936
Old 05-01-2019, 04:36 PM
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